The invention relates to a fluid filter for a fuel.
A known fuel filter includes a housing having at least one inlet connector and at least one outlet connector for a fluid to be filtered, a middle tube located in the housing, a filter element arranged in the housing, the filter element consisting of a band-shaped filter material wound spirally around the middle tube to form a plurality of complete turns including an outermost complete turn, opposing end faces of the filter element on opposite ends thereof and spaces between the turns, which open towards the opposite end faces and which communicate with the connectors, and a bottom cover cap which engages the filter element.
Such a fluid filter is already known from WO-Al 0, 081, 597, especially FIG. 2. In this fuel filter a wound filter element is arranged in a housing and has a funnel-shaped cover cap on its bottom end face on the clean side of the fuel filter. This cover cap deflects the purified fluid flow coming out of the end face into the middle tube. At the same time, inwardly pressed radial ribs supporting the filter element are arranged in the cover cap. A disadvantage of this fluid filter is that this cover cap consists of metal and has a sleeve-shaped edge portion which is widened in a funnel-shaped manner and into which the wound filter element is simply pressed with its outer surface. By this simple pressing of the filter element into the cover cap, a serviceable sealing between the dirty side and clean side of the filter can be achieved, in the region of the compressed outer surface, only with oils having substantially higher viscosities than petrol or diesel fuels. Moreover, when the filter element is being pressed in, the outer layers of the winding usually consisting of paper are excessively compressed or even damaged. Furthermore, the metal cover cap necessitates an increased outlay in terms of material and machining. Besides, the distance between the cover cap and the bottom of the housing not only results in a poor utilisation of space, but is also unsuitable for different models in which an additional connection has to be provided at the bottom of the housing. In addition, because of the assembly of a large number of individual parts, the construction of the filter is cost-intensive.
Further, German Patent Specification 3,513,062 makes known a fluid filter, in the housing of which a wound filter element is arranged with the help of a cover cap. Here, the wound filter element and the cover cap are already appropriately preassembled with one another in a fluid-tight manner. A disadvantage, however, is that the cover cap is arranged on the upper end face of the wound filter element and this cover cap bounds with a housing lid an additional inflow space. Moreover, in this design of the cover cap a series of sealing points between the dirty side and clean side are necessary. At the same time, one of these sealing points between the cylindrical outer surface of the wound filter element and an associated cylindrical inner wall at a tubular extension of the cover cap can be produced only with difficulty, especially as there is no axial fixing of these two parts relative to one another. Besides, an additional adhesive bond is required between the filter insert and filter housing to separate the dirty side and clean side.
Further, German Patent Specification 2,256,995 makes known a fluid filter with a wound filter element, in which the prefabricated filter element is bedded into the bottom-shaped housing lower part. Here, the prefabricated filter element possesses, on its cylindrical outer surface, a preformed annular bead of hot-melt adhesive which is oversized in relation to the inner wall of the housing and which, when the wound filter element is pressed into a heated housing part, melts in its outer edge zone and, after solidifying, makes a firm sealing connection between the dirty side and clean side. But it can be a disadvantage that this connection between the filter winding and housing is possible only by an adhesive. For a perfect connection, the bowl-shaped housing part must be cleaned so as to be absolutely free of grease before the wound filter element is bedded in, thereby increasing the production outlay. During any intermediate storage of the filter element, its two end faces are exposed without protection to contamination.